I don't think that JAV is losing its edge, but it does seem to me that its going through a dip or slump right now. For one I don't think that the industry has any top tier JAV idols to carry the industy like they have in the pass. Yes they have handful of popular JAV idols, but their a combination of the leftover (for lack of a better word) from the previous generation and some up an comes. They don't seem to have those main stream appeal JAV idols to carry the industry. In the pass JAV idols like Sora Aoi, Yuma Asami, Maria Ozawa, Nana Ogura, Rio Hamasaki, Yua Aida are just some among a group of 10-15 JAV idols of their generation that form the backbone of the industry. Right now i don't see many JAV idols that have debut within the last couple of year what have made the same impact as those girls did when they first debut and the following couple of years. Even the girls that have make a big impact when they debut, they either burn out quickly or lose a lot of stream after a good year or two. As for the Idols like Kirara Asuka, Julia , Tsubomi, Hitomi I associate them with the tail end of the time of the super idols of the likes of Sora Aoi, Yuma Asami among other. Which just show you how long they have been around. I huge fan of them, and i still enjoy watching their new videos but it can be hard for them to hold the same high level of attention and excitement of their fans over a larger period of time.
It could also be a side effect of the fact that every year so many new girls debut. Some seem to just want to make a quick buck or two. While others don't see the future they wanted when they first got into the industry. They where probably hoping to hit it big, but after a couple of movies and a luke warm reception they rather cut their loss an get out rather than get pay less than they think they should be getting pay.
Another possibility is that so many cute, hot, and sexy idols debut each year. That we have just become somewhat desensitize to all JAV idols what we are just expecting too much for each girl from the start. So when we see an average performances we quickly lose interest and move on to the next cute/hot/sexy idol that just debut who is the next big thing. As a result we don't get to see jav idols develop and come to their own, because they weren't A+ performers from the get go, like some other girl we saw debut at the same time. At the same time we lose interest on the "it girl" we left some other new idols for because she either had a really luck and good first debut and everything after that is sub-par. Quick example Yua Mikami. I really like her debut movie and TEK-073 movie, but besides those two movies every think else has been average at best. I think that Yua Mikami has everything she needs to be a top star and as of right now is under performing especially compare to her full potential. The same can be said of so many idols out their. I think that is way it seems that JAV is losing it's edge. Especially given that the larger studious producing the same top tier and quality of JAV films and Idols as they did in the past. The bigger studious right now just seem to be buying what they see as top talent idols. Who actually build their name and career at smaller labels and movie genres. Only to be tame and piggen hole into fitting into the what the type of movies that larger studios like to produce. those are my two cents.